Explanation for the 9500i's sudden ramp-up...
Hi everyone,
As I mentioned in my previous thread,
My new 9500i -- My Preliminary Review,
I found that the Escort 9500i features a "signal strength anticipator" circuit, for lack of a better name since this circuit is undocumented both in the user manual and on Escort's web site. I also don't know whether this circuit is implemented via hardware or via firmware, but my money is on a firmware implementation. In any event, this "signal strength anticipator" circuit is what frequently causes the signal strength on a 9500i to suddenly jump from a low signal strength reading to a very high signal strength reading within a second or two. Note that this only occurs whenever the 9500i encounters anything but a relatively steady or slowly increasing radar signal.
After talking with Escort customer service and describing how the 9500i can suddenly indicate a very strong signal whenever any detected signal is rapidly increasing in signal strength, Escort's customer service representative confirmed that this circuit is by design and that its purpose is to generate a strong warning whenever radar is encountered which is fairly rapidly or rapidly rising in signal strength. The Escort CS representative also indicated that the circuit works like what I am about to describe further below.
I just received my 9500i yesterday and haven't had the time to measure the integration time interval for this "signal strength anticipator" ciruit. Thus all time intervals are merely good geusses by me. Nevertheless I did take an hour of time to perform several tests in order to determine how this circuit works. My trusty cell phone, which only puts out a continuous X band signal when it is powered off yet charging, turned out to be very handy for determining exactly how this "signal strength anticipator" ciruit works. Additionally, I also performed several tests in my local Lowe's and Wal-Mart parking lots and noted how large passing vehicles could momentarily reflect a strong radar signal from a pair of door openers and suddenly trigger a falsely strong signal strength reading on my 9500i.
Escort's obvious ideas which lead to this circuit...
Before I present a graph and describe how this "signal strength anticipator" ciruit works, I feel that I should describe why Escort incorporated such a circuit into the 9500i. I've had all night and most of today to really think about the circuit's purpose. Imagine encountering police radar around a curve or over a hill. In such circumstances, you normally would get a weak warning for the hidden radar gun. As you start rounding the curve or start cresting the hill, any other radar detector will begin to fairly rapidly indicate an increasing signal strength. By the time you react, it may be too late if suddenly the radar gun and patrol car become visible to you and the radar gun has your speed since the situation has now changed to line of sight. On the other hand, Escort's "signal strength anticipator" ciruit would warn you with a sudden and much stronger warning well before you rounded the curve or crested the hill. Why? Because the "signal strength anticipator" ciruit would have seen the more rapidly increasing signal strength, then extrapolated the slope of the signal strength rise to anticipate what the signal strength would theoretically be after another two seconds, and generate a much stronger alert based on the extrapolated future signal strength!
So, when you think about it, Escort's "signal strength anticipator" ciruit actually is a pretty neat idea with the specific purpose of strongly alerting you to around-the-curve and over-the-hill radar threats. In short, the purpose of this circuit is to give you a strong warning in such situations and save you from a speeding ticket. Hmm, maybe I should call this circuit the "anti-speed trap circuit" since most drivers get nailed in over-the-hill and around-the-corner speed traps. Yet "anticipator" more accurately describes how this circuit operates.
How this "signal strength anticipator" circuit works...
Well, lets get to the meat of this post -- exactly how this circuit works and why it can cause the signal strength to suddenly jump from a weak signal to a strong signal. First, I will briefly present my theory about how the circuit operates, then present my graph, and then fully explain my graph.
Basically, the "signal strength anticipator" circuit looks at the signal strength of the detected radar signal over a very short time interval. I haven't measured the time interval, but 1/2 second appears to be a good guess based on my initial observations. The circuit notes the signal strength of the radar at the beginning and end of this 1/2 second interval and immediately calculates the slope for the rate of increase in the detected radar signal. The circuit then extrapolates this sloped line over a longer interval in order to anticipate how strong the radar signal would be at the end of this longer interval. I am guessing that the circuit calculates what the projected radar signal strength would be about 2 seconds later. In other words, this circuit looks at the rate of change in the radar signal strength intensity during a very short interval, and then predicts how strong the radar signal would be if this rate of change continued over an additional 2 seconds.
Still don't get it? Well, here is my graph to demonstrate the basic principles of how the "signal strength anticipator" circuit works:
http://www.mem-tek.com/radar/Escort_...ator_chart.gif
I designed this chart based on my 9500i testing yesterday. This chart specifically shows an example of turning into a Lowe's parking lot such that my 9500i, after completion of a 90 degree turn, ended up pointed directly towards the Lowe's store's K band microwave door openers. Prior to the 90 degree turn, my 9500i was indicating a K band signal strength of 2 on its display. Immediately after the 90 degree turn and after immediately parking in a nearby parking space with my 9500i fully facing the door openers, and after waiting for several seconds for the indicated signal strength to "settle down", the 9500i continuouslly indicated a signal strength of 5. Its what my 9500i displayed during the 90 degree turn that is interesting.
Note the solid black curve in my above graph. This curve is basically what my Bel STi showed in terms of signal strength during the 90 degree turn, and is what any radar other detector should basically show when making the 90 degree turn into a parking lot with microwave door openers. The 9500i instead produced the signal strength curve shown in dark gold. Why? Its due to the 9500i's "signal strength anticipator" circuit"!
While just starting the 90 degree turn, the 9500i's "anticipator" circuit calculated the radar signal slope during the time interval shown in the light green band within the above graph. The dark green dots indicate the radar signal strength at the beginning and end of the time window shown in light green. From these two dark green points, the circuit extrapolated the dark green line which as a slope which is the same as the two dark green points. The circuit then calculates how strong the signal would be two seconds later from the beginning of time interval used to find the slope. This is shown as a dark green square that indicated the anticipated signal strength two seconds after the beginning of the time interval used to find the two points for the slope.
For the light green and light purple time intervals, note that the "anticipator" circuit's anticipated signal strength 2 seconds later is very similar to the actual current signal strength shown by the black curve. Now see that the light blue shaded interval obviously has an increasing yet still fairly moderate slope. The "anticipator" circuit during the blue interval estimates that the radar signal will have a signal strength of nearly 4 around 2 seconds later.
The light red interval is what gets interesting. During the red 1/2 second interval, the "anticipator" circuit calculates a rather steep slope, and anticipates that 2 seconds later the radar signal should nearly be a solid 9 out of 10! This clearly nowhere matches the actual radar strength shown by the black curve, but it would give you a strong warning for radar around a curve or over a hill!
The light orange interval is nearly at the end of the 90 degree turn into the parking lot. At this point, the 9500i is nearly facing the microwave door openers. Thus the slope is rapidly smoothing out until the point where the 9500i is directly facing the microwave door openers.
Look again at where the colored squares in the above chart are positioned. Each colored square represents the anticipated signal strength 2 seconds later after the beginning of each 1/2 second integration interval, or 1-1/2 seconds after the end of each 1/2 second long integration interval. Thus I drew a thin and appropriately colored horizontal line, backwards and toward the left from each square for 1-1/2 seconds, to indicate the point in time and signal strength intensity which the "anticipator" circuit has calculated. I then drew a dark gold colored and smoothed curve which shows what my 9500i actually displayed in terms of signal strength, due to the effects of its "anticipator" circuit.
Why doesn't the gold curve representing the anticipated and reported signal strength rapidly drop off in order to meet the backwards exrapolated thin orange horizontal line? Because the 9500i, like most radar detectors, also features a simple RC circuit which smooths out the signal strength display, and which introduces a time delay for the fade of the detected radar signal. For example, I have an old Maxim RD-25 radar detector which, upon killing power to a radar test source, takes nearly a full 10 seconds for its display to wind back down to zero! Thus, once the 9500i's indicated signal strength has been nearly pegged out by its "anticipator" circuit, it takes several seconds for the 9500i's display to "settle down" to a much lower and accurate signal strength.
Well, I hope that I have done a good job explaining how the 9500i's "signal strength anticipator" circuit works. Again, for relatively steady radar signals and for radar signals which are only slowly increasing in signal strength, the 9500i will correctly display the signal strength throughout the entire display range. Its only when a sudden and rapidly increasing radar signal is encountered, regardless if its strength, that the 9500i will indicate a much stronger radar signal compared to the actual current intensity of the radar signal.
So, is this "signal strength anticipator" circuit a benefit? Yes, for radar located over a hill or around a curve, or whenever a patrol car makes a sudden turn such that its radar gun is pointed towards your 9500i. Yet this circuit does lead to annoyingly strong falses whenever you make a turn into a shopping center, whenever shopping center door openers suddenly become unmasked by nearby buildings, or whenever a police radar gun suddenly becomes unmasked by surrounding terrain or other vehicles between your 9500i and the radar gun.
Personally, I find Escort's "signal strength anticipator" circuit to be more annoying rather than beneficial since I am old school and would prefer that my 9500i would always accurately report the detected signal strength rather than this circuit's anticipated signal strength.
Best Regards,
--Michael
